Add Projector Obs to LGPU

[maliasadi]

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---

Context:
Add support for Projector observable via diagonalization to LGPU.

Description of the Change:

Benefits:

Possible Drawbacks:

Related GitHub Issues:

Fixes #883
[sc-72652]

[github-actions]

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[codecov]

Codecov Report

Attention: Patch coverage is 58.82353% with 7 lines in your changes missing coverage. Please review.

Project coverage is 82.97%. Comparing base (a36fe22) to head (6e6472c).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
pennylane_lightning/lightning_gpu/lightning_gpu.py	56.25%	7 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (a36fe22) and HEAD (6e6472c). Click for more details.

HEAD has 7 uploads less than BASE

Flag	BASE (a36fe22)	HEAD (6e6472c)
	15	8

Additional details and impacted files

@@             Coverage Diff             @@
##           master     #894       +/-   ##
===========================================
- Coverage   96.25%   82.97%   -13.29%     
===========================================
  Files         212       24      -188     
  Lines       28020     2162    -25858     
===========================================
- Hits        26972     1794    -25178     
+ Misses       1048      368      -680     

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[vincentmr]

Nice @maliasadi . Could we just remove this condition and instead filter only on the device name (like LTensor)? I think it would make it more obvious whether the device should support the feature or not.

[maliasadi]

@vincentmr Nice catch! We can actually remove this condition from those unit tests.

[multiphaseCFD]

Thanks @maliasadi ! Looks good to me.

[multiphaseCFD]

Nice work! Thanks @maliasadi !

[vincentmr]

LGTM, nice short and sweet change. Thanks @maliasadi .